An image sensor and a method for manufacturing the same are provided. In the image sensor, a semiconductor substrate has a pixel region and a peripheral region defined by a first device isolation layer. First and second photodiode patterns are formed on the pixel region and are connected to lower metal lines to first and second readout circuitries. The first photodiode pattern performs as an active photodiode and the second photodiode pattern functions as a dummy pixel. The dummy pixel can measure leakage current.